 /*******************************************************************************
  * Copyright (c) 2005, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.ui.internal.ide;

 import org.eclipse.core.runtime.IProgressMonitor;
 import org.eclipse.core.runtime.IStatus;
 import org.eclipse.core.runtime.Platform;
 import org.eclipse.core.runtime.Status;
 import org.eclipse.core.runtime.jobs.Job;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.SWTException;
 import org.eclipse.swt.widgets.Display;
 import org.eclipse.swt.widgets.Event;
 import org.eclipse.swt.widgets.Listener;
 import org.eclipse.ui.PlatformUI;
 import org.eclipse.ui.application.IWorkbenchConfigurer;

 /**
  * The idle helper detects when the system is idle in order to perform garbage
  * collection in a way that minimizes impact on responsiveness of the UI.
  * The algorithm for determining when to perform a garbage collection
  * is as follows:
  *
  * - Never gc if there is a test harness present
  * - Don't gc if background jobs are running
  * - Don't gc if the keyboard or mouse have been active within IDLE_INTERVAL
  * - Don't gc if there has been a GC within the minimum gc interval (system property PROP_GC_INTERVAL)
  * - After a gc, don't gc again until (duration * GC_DELAY_MULTIPLIER) has elapsed.
  * For example, if a GC takes 100ms and the multiplier is 60, don't gc for at least five seconds
  * - Never gc again if any single gc takes longer than system property PROP_GC_MAX
  */
 class IDEIdleHelper {

     /**
      * The default minimum time between garbage collections.
      */
     private static final int DEFAULT_GC_INTERVAL = 60000;

     /**
      * The default maximum duration for a garbage collection, beyond which
      * the explicit gc mechanism is automatically disabled.
      */
     private static final int DEFAULT_GC_MAX = 8000;

     /**
      * The multiple of the last gc duration before we will consider doing
      * another one.
      */
     private static final int GC_DELAY_MULTIPLIER = 60;

     /**
      * The time interval of no keyboard or mouse events after which the system
      * is considered idle.
      */
     private static final int IDLE_INTERVAL = 5000;

     /**
      * The name of the boolean system property that specifies whether explicit
      * garbage collection is enabled.
      */
     private static final String PROP_GC = "ide.gc"; //$NON-NLS-1$

     /**
      * The name of the integer system property that specifies the minimum time
      * interval in milliseconds between garbage collections.
      */
     private static final String PROP_GC_INTERVAL = "ide.gc.interval"; //$NON-NLS-1$

     /**
      * The name of the integer system property that specifies the maximum
      * duration for a garbage collection. If this duration is ever exceeded, the
      * explicit gc mechanism is disabled for the remainder of the session.
      */
     private static final String PROP_GC_MAX = "ide.gc.max"; //$NON-NLS-1$

     protected IWorkbenchConfigurer configurer;

     private Listener idleListener;

     /**
      * The last time we garbage collected.
      */
     private long lastGC = System.currentTimeMillis();

     /**
      * The maximum gc duration. If this value is exceeded, the
      * entire explicit gc mechanism is disabled.
      */
     private int maxGC = DEFAULT_GC_MAX;
     /**
      * The minimum time interval until the next garbage collection
      */
     private int minGCInterval = DEFAULT_GC_INTERVAL;

     /**
      * The time interval until the next garbage collection
      */
     private int nextGCInterval = DEFAULT_GC_INTERVAL;
     
     private Job gcJob;

     private Runnable handler;
     
     /**
      * Creates and initializes the idle handler
      * @param aConfigurer The workbench configurer.
      */
     IDEIdleHelper(IWorkbenchConfigurer aConfigurer) {
         this.configurer = aConfigurer;
         //don't gc while running tests because performance tests are sensitive to timing (see bug 121562)
 if (PlatformUI.getTestableObject().getTestHarness() != null) {
             return;
         }
         String enabled = System.getProperty(PROP_GC);
         //gc is turned on by default if property is missing
 if (enabled != null && enabled.equalsIgnoreCase(Boolean.FALSE.toString())) {
             return;
         }
         //init gc interval
 Integer prop = Integer.getInteger(PROP_GC_INTERVAL);
         if (prop != null && prop.intValue() >= 0) {
             minGCInterval = nextGCInterval = prop.intValue();
         }

         //init max gc interval
 prop = Integer.getInteger(PROP_GC_MAX);
         if (prop != null) {
             maxGC = prop.intValue();
         }
         
         createGarbageCollectionJob();

         //hook idle handler
 final Display display = configurer.getWorkbench().getDisplay();
         handler = new Runnable () {
                     public void run() {
                         if (!display.isDisposed() && !configurer.getWorkbench().isClosing()) {
                             int nextInterval;
                             final long start = System.currentTimeMillis();
                             //don't garbage collect if background jobs are running
 if (!Platform.getJobManager().isIdle()) {
                                 nextInterval = IDLE_INTERVAL;
                             } else if ((start - lastGC) < nextGCInterval) {
                                 //don't garbage collect if we have collected within the specific interval
 nextInterval = nextGCInterval - (int) (start - lastGC);
                             } else {
                                 gcJob.schedule();
                                 nextInterval = minGCInterval;
                             }
                             display.timerExec(nextInterval, this);
                         }
                     }
                 };
         idleListener = new Listener() {
             public void handleEvent(Event event) {
                 display.timerExec(IDLE_INTERVAL, handler);
             }
         };
         display.addFilter(SWT.KeyUp, idleListener);
         display.addFilter(SWT.MouseUp, idleListener);
     }

     /**
      * Creates the job that performs garbage collection
      */
     private void createGarbageCollectionJob() {
         gcJob = new Job(IDEWorkbenchMessages.IDEIdleHelper_backgroundGC) {
             protected IStatus run(IProgressMonitor monitor) {
                 final Display display = configurer.getWorkbench().getDisplay();
                 if (display != null && !display.isDisposed()) {
                     final long start = System.currentTimeMillis();
                     System.gc();
                     System.runFinalization();
                     lastGC = start;
                     final int duration = (int) (System.currentTimeMillis() - start);
                     if (Policy.DEBUG_GC) {
                         System.out.println("Explicit GC took: " + duration); //$NON-NLS-1$
 }
                     if (duration > maxGC) {
                         if (Policy.DEBUG_GC) {
                             System.out.println("Further explicit GCs disabled due to long GC"); //$NON-NLS-1$
 }
                         shutdown();
                     } else {
                         //if the gc took a long time, ensure the next gc doesn't happen for awhile
 nextGCInterval = Math.max(minGCInterval, GC_DELAY_MULTIPLIER * duration);
                         if (Policy.DEBUG_GC) {
                             System.out.println("Next GC to run in: " + nextGCInterval); //$NON-NLS-1$
 }
                     }
                 }
                 return Status.OK_STATUS;
             }
         };
         gcJob.setSystem(true);
     }

     /**
      * Shuts down the idle helper, removing any installed listeners, etc.
      */
     void shutdown() {
         if (idleListener == null) {
             return;
         }
         final Display display = configurer.getWorkbench().getDisplay();
         if (display != null && !display.isDisposed()) {
             try {
                 display.asyncExec(new Runnable () {
                     public void run() {
                         display.timerExec(-1, handler);
                         display.removeFilter(SWT.KeyUp, idleListener);
                         display.removeFilter(SWT.MouseUp, idleListener);
                     }
                 });
             } catch (SWTException ex) {
                 // ignore (display might be disposed)
 }
         }
     }
 }
